The UCLA Center of the Multicenter AIDS Cohort Study (MACS) requests a continuation of support from April 1, 1993 through March 31, 1995 to facilitate its continued participation in the MACS. Since 1984, the UCLA Center has followed a cohort of 1,637 homosexual/bisexual men every three to six months for changes in behavioral, clinical, immunologic, virologic, and neuropsychologic factors. During that time, 130 men have become infected by HIV-1 and 456 men have developed AIDS including 29 of the men who seroconverted after the first visit. We know the current status of over 85 percent of the men still living and ever 75 percent of the men in the original cohort are still seen at least once a year. The UCLA Center of the MACS has collaborated with the investigators at the other four centers of the MACS and with the Division of AIDS, National Institute of Allergy and Infectious Diseases in the publication of more than one hundred research papers on all aspects of AIDS in homosexual/bisexual men and, in addition, has published specific papers based on studies of the men in the UCLA cohort. These papers have elucidated many of the basic mechanisms involved in the infection and progression of HIV-1 infection to AIDS and death. The UCLA Center of the MACS is proposing to continue these studies with special emphasis on the immunologic, virologic, and behavioral factors which promote the progression of HIV-1 infection to AIDS, as well as on the spectrum of disease manifestations resulting from HIV-1 infection (including malignancies) and the impact of treatment on both the course of disease and the spectrum of disease manifestations. The UCLA Center now includes twenty-three outstanding investigators in epidemiology, immunology, virology, pathology, neuropsychology, and clinical AIDS. The proposed UCLA Center investigations are specifically designed to elucidate the relationships between alterations in immune function, immune deficiency, viral structure and load, and the clinical/pathological course of HIV-1 infection. These investigations are enhanced by the close collaboration of the UCLA investigators both among themselves and with investigators at the other centers.